Effect of expanded CD4⁺CD25^high T cells on the alloresponse of antigen-experienced responder T cells. Expanded CD4⁺CD25^high T cells suppress the alloresponse of antigen-experienced responder T cells. Sorted CD4⁺CD25^- T cells were expanded with anti-CD3/anti-CD28–coated beads, rested for 2 days, and then stimulated with irradiated allogeneic PBMCs in the absence or presence of autologous expanded CD4⁺CD25^high or CD25^- T cells at a 1:1 ratio for 5 days. ^***P < .001(Student t test). ^*P < .05. One of 3 independent experiments using cells from different donors.